German published patent application DE 19414046, for example, discloses an electromechanically operable parking brake of this general type. The special feature of the prior art parking brake includes that the rotor of the electric motor has a hollow or tubular design and radially embraces the gear unit. This method permits achieving an actuating unit which exhibits a small axial overall length. However, the state of the art mentioned does not indicate how the actuating unit is driven.
An object of the present invention is to disclose a method and a system for actuating an electromechanically operable parking brake which permits adjusting necessary nominal values of the actuating force. Another object of the present invention involves disclosing a method and a system which allow release of the parking brake and adjustment of the lining clearance. Still another objective is directed to monitoring the proper function or monitoring that predetermined limit values (such as maximum current, power requirement) are maintained.
According to the present method, this object is achieved in that the current to be supplied to the actuator and the actuator position are evaluated in order to determine the voltage that is to be applied to the actuator corresponding to the desired actuating force and the actuating force gradient.
To render the idea of the present invention more precise, a desired actuator position and a desired actuator rotational speed is associated with the desired actuating force and its gradient by function control and monitoring.
In this arrangement, the desired actuator position and the desired actuator rotational speed are preferably subjected to a position control in order to produce a signal representative of the actuator current nominal value.
The voltage that is to be applied to the actuator is preferably calculated by evaluating the signal representative of the desired actuating current value in consideration of a signal representative of the actuator rotational speed actual value.
Another favorable feature of the method of the present invention includes that a second voltage value, which preferably amounts to 0 volt, can be applied to the actuator in dependence on a switching variable.
The switching variable can be set by the function control and monitoring system due to error and/or functional reasons, or by the position control due to functional reasons.
An actuation system according to the present invention for implementing the above-mentioned method is characterized in that
a) there is provision of a function controlling and monitoring module which is furnished, as input quantities, with nominal values of the actuating force and signals representative of the actuating force gradient, with a signal representative of the actual actuator position, and a signal representative of the actual actuator current, and which produces from the input quantities the nominal value of the actuator rotational speed, the nominal value of the actuator position and the actual value of the actuator rotational speed, PA1 b) there is provision of a position controller which is furnished, as input quantities, with the signals that correspond to the nominal and actual value of the actuator rotational speed and the nominal and actual value of the actuator position, and which provides the signal representative of the actuator current nominal value, and PA1 c) connected downstream of which is a calculating module in which the signal representative of the actuator current nominal value is converted into the desired voltage that is to be applied to the actuator, and in which there occurs a compensation of the opposing electromagnetic force generated by the actuator, in consideration of the actual value of the actuator rotational speed.
In this arrangement, it is assumed that elements which exhibit a self-locking effect are provided in the electromechanical driving track. A simplified control structure compared to a system without self-locking is achieved by specifically utilizing the self-locking effect in the actuator activation. It is not required to actuate the electric parking brake in a controlled way when a predetermined target position or target force is reached; it may rather be brought to a standstill in a simple manner by the influence of a great degree of static friction. Due to the self-locking effect, the parking brake will remain in this position also in the deenergized condition.
In a preferred aspect of the actuation system of the present invention, switching means are connected downstream of the calculating module which permit applying a second voltage value to the actuator, that is preferably 0 volt, in dependence on a switching variable.
In another embodiment of the system of the present invention, the output signal of the switching means is sent to an electronic actuating circuit (servo booster) whose output signal is used to drive the actuator.